Light-driven Metal-catalyzed Asymmetric Transformations

Identifier:  TDX:3222

Handle: https://hdl.handle.net/20.500.11797/TDX3222

Authors:  Gandolfo, Eugenio

Abstract:
Abstract An excited-state molecule offers a completely different reactivity than in its ground state. It can be both a better oxidant and a better reductant, thus enabling novel transformations due to the ability to generate radical intermediates under mild conditions. The main scientific objective of this doctoral thesis was to investigate the direct excitation of substrates and intermediates to unlock novel reactivity manifolds, enabling asymmetric metal-catalyzed transformations unfeasible under the thermal domain. To this end, I exploited the chemistry of 4-alkyl-1,4-dihydropyridines (4-alkyl-DHPs) in either their excited- and ground-state as sources of electrons and radical precursors. In the first project, I exploited the excited-state properties of 4-alkyl-DHPs, serving as strong photoreductant and radicals source, to enable an asymmetric nickel-catalyzed acyl cross-coupling to access highly enantioenriched α,α-disubstituted ketones. In the second project, I studied how, by means of light-excitation, it was possible to divert the established ground-state reactivity of an organoiridium chiral complex, enabling mechanistically original processes unattainable in the thermal domain. In particular, we probed a particular chiral η3-allyliridium(III) complex for which we estimated an oxidation potential of ̴ +1.24 V in the excited state. This novel catalytic function acquired upon light excitation was exploited to develop an enantioselective alkyl-alkyl cross-coupling between benzyl allylic alcohols and α-amino radicals, derived from 4-alkyl-DHPs serving as ground-state radical sources.